300 CHEMICAL ENGINEERING filters, if suitable. If deep frames are used and "through washing" is employed, 4 that is introducing the wash fluid between the partition center of a plate and the filtering medium and forcing it through the cake to the similar recess on the other FIG. 22.—Feed eye of plate. side, using every other discharge orifice or cock; then if the cake formed is of a loose character and offers little resistance to pressure or tends to build up slowly leaving open spaces in the center of the frame there will be a tendency to bulge the filtering medium and an excessive strain will be put upon it shortening its life. Simple washing is better in such cases. The section, Fig. 24, shows one way of attaining " through washing" by the "every other cock" method. Separate filtrate and wash orifices or cocks should be employed where possible, as with this way of working if anything happens to the filtering operation at any CLOSED OPCM CUMEO OPS*. FIG. 24.—"Through" washing. point it will be detected at once. If any leaf is filtering badly from irregularity of cake accumulation which can be detected by cloudiness in the issuing filtrate the particular cock or cocks involved can be shut off until the cake has accumulated to a thickness to yield a clear filtrate. With volatile liquids cocks cannot be used as the filtrate or wash of this kind must be led to a closed vessel to avoid loss by evaporation. If there is a volatile wash following the cake formation it will be desirable to have a special outlet for it. In case there are no cocks there are two channels, each of which drops in to alternate plates. In fact when special eyes for steam, etc., are also considered the possible combinations are almost endless and it is best to consult the manufacturers where there is an involved washing necessary, in order to obtain the most suitable leaves.